Metal oxide having a spinel-type crystal structure, method for producing the same, method for reducing carbon dioxide, and apparatus for reducing carbon dioxide.

Abstract

Provided are: a carbon dioxide reduction catalyst that can reduce carbon dioxide under mild conditions; a carbon dioxide reduction method using the carbon dioxide reduction catalyst; and a carbon dioxide reduction apparatus. The metal oxide according to the present invention has a spinel-type crystal structure comprising a metal element A, manganese and oxygen. The A comprises at least one metal element selected from the group consisting of nickel and copper, the (manganese) / (oxygen) molar compositional ratio is 1:1.8 to 1:2.2, and the (metal element A) / (manganese) molar compositional ratio is 1:1.7 to 1:2.3. The metal oxide is characterized in that the ratio of the intensity of a peak having a 2θ value of 16° to 20° (P18°) to the intensity of a peak having a 2θ value of 35° to 39° (P37°) in an X-ray diffraction pattern obtained by an X-ray diffraction measurement using Cu-Kα line, i.e., I18° / I37°, is 0.2 or more.

Description

[Technical Field]

[0001] The present invention relates to a metal oxide having a spinel-type crystal structure, a method for producing the same, a method for reducing carbon dioxide using the metal oxide, and a carbon dioxide reduction apparatus. [Background technology]

[0002] The burning of fossil fuels in various plants and other facilities is a major cause of carbon dioxide emissions, leading to problems such as global warming due to the rising concentration of carbon dioxide (CO2) in the atmosphere. On the other hand, carbon monoxide is produced using fossil fuels as raw materials. When natural gas is used as a raw material for carbon monoxide, a mixed gas of carbon monoxide and hydrogen is obtained by steam reforming the natural gas, and this mixed gas is further used as a raw material for various chemical products.

[0003] To address the problem of massive carbon dioxide emissions, reactions that reduce carbon dioxide to carbon monoxide (CO) are attracting attention. Within this context, research into catalysts for carbon dioxide reduction is particularly active worldwide. Among these, many metal oxides have been reported to possess excellent properties as carbon dioxide reduction catalysts.

[0004] For example, Non-Patent Document 1 discloses a carbon dioxide reduction catalyst using a spinel-type metal oxide such as Co3O4.

[0005] Furthermore, Patent Document 1 discloses a carbon dioxide reduction catalyst using spinel-type composite metal oxides such as CuCo2O4 and MnCo2O4.

[0006] Furthermore, Non-Patent Document 2 discloses a carbon dioxide reduction catalyst using Ge-doped CeO2. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2021-23840

Non-Patent Literature

[0008]

Non-Patent Literature 1

Non-Patent Literature 2

Summary of the Invention

Problems to be Solved by the Invention

[0009] By the way, the carbon dioxide reduction method of Non-Patent Literature 1 utilizes electrochemical reduction. Therefore, it consumes electrical energy. The carbon dioxide reduction method of Patent Literature 1 utilizes photoreduction. Therefore, it is necessary to use it together with a light absorber that absorbs light and converts it into electron energy. The carbon dioxide reduction method of Non-Patent Literature 3 utilizes reduction while heating with microwaves. Therefore, a microwave power supply is required. Therefore, an object of the present invention is to provide a carbon dioxide reduction catalyst capable of reducing carbon dioxide under mild conditions, a carbon dioxide reduction method using the carbon dioxide reduction catalyst, and a carbon dioxide reduction device. Another object of the present invention is to focus on the energy consumed in the manufacturing method of the carbon dioxide reduction catalyst from a total perspective in addition to reducing the energy required for the carbon dioxide reduction method, and to provide a catalyst manufacturing method at a lower temperature.

Means for Solving the Problems

[0010] The configuration of the present invention for solving the above problems is as follows. [1] A metal oxide having a spinel-type crystal structure, comprising metal element A, manganese, and oxygen, The aforementioned A is at least one metallic element selected from the group consisting of nickel, magnesium, zinc, copper, and iron. The molar composition ratio of manganese to oxygen is 1:1.8 to 1:2.2. The molar composition ratio of metal element A to manganese is 1:1.7 to 1:2.3. The aforementioned metal oxide exhibits a peak (P) in the X-ray diffraction pattern obtained by X-ray diffraction measurement using Cu-Kα rays, where the 2θ value is in the range of 16° to 20°. 18° ) and the peak (P) where the 2θ value is in the range of 35°~39° 37° ) and the intensity ratio (I 18° / I 37° A metal oxide characterized by having a value of 0.2 or higher. Preferably, A is at least one metallic element selected from the group consisting of nickel and copper. [2] The metal oxide is a peak (P) in the X-ray diffraction pattern obtained by X-ray diffraction measurement using Cu-Kα rays, where the 2θ value is in the range of 16 to 20 degrees. 18° A metal oxide as described in [1], wherein the full width at half maximum (FWHM) of the ) is 1.0° to 7.0°. [3] The metal oxide described in [1] or [2], having an average particle size of 1 to 10 nm. [4] A metal oxide according to any of [1] to [3], including a compound represented by formula (1). AMn2O4(1) (In formula (1), A is at least one element selected from the group consisting of Ni and Cu, which is the same as the aforementioned metal element A.) [5] A method for producing a metal oxide as described in any of [1] to [4], A first step involves preparing a mixture containing permanganate, a metal salt of the aforementioned metal element A, and an alcohol. The mixture obtained in the first step is stirred and reacted at a temperature below the melting point of the alcohol in the second step, and includes, A is at least one metallic element selected from the group consisting of nickel and copper. The molar ratio (A:Mn) of the amount of metal salt of metal element A charged to the amount of permanganate charged, in terms of metal elements, is 1:1.7 to 1:2.3. A method for producing metal oxides, characterized by the following: [6] A method for producing a metal oxide having a spinel-type crystal structure, comprising metal element A, manganese, and oxygen, A first step involves preparing a mixture containing permanganate, a metal salt of the aforementioned metal element A, and an alcohol. The mixture obtained in the first step is stirred and reacted at a temperature below the melting point of the alcohol in the second step, and includes, A is at least one metallic element selected from the group consisting of nickel and copper. The molar composition ratio of manganese to oxygen is 1:1.8 to 1:2.2. The molar composition ratio of metal element A to manganese is 1:1.7 to 1:2.3. A method for producing metal oxides, characterized by the following: [7] The permanganate is tetrabutylammonium permanganate, A method for producing a metal oxide according to [5] or [6], wherein the metal salt is at least one selected from the group consisting of nickel chloride and copper chloride. [8] A third step in which the reaction solution obtained in the second step is filtered to obtain the metal oxide precursor, A fourth step involves heat-treating the precursor obtained in the third step at a temperature of 20°C to 300°C, A method for producing a metal oxide, further comprising the method described in any of [5] to [7]. [9] A metal oxide obtained using the method for producing a metal oxide described in [6].

[10] A carbon dioxide reduction catalyst containing a metal oxide as described in any of [1] to [4] or [9].

[11] A method for reducing carbon dioxide using a metal oxide described in any of [1] to [4] or [9], A method for reducing carbon dioxide, characterized in that the reaction temperature in the carbon dioxide reduction reaction is 300°C or lower.

[12] A carbon dioxide reduction device that reduces carbon dioxide, The carbon dioxide inlet and A reaction section equipped with a carbon dioxide reduction catalyst, A heating section for heating the above reaction section, Equipped with, The carbon dioxide reduction catalyst contains a metal oxide described in any of [1] to [4] or [9]. A carbon dioxide reduction device characterized by the following features.

[0011]

[13] A positive electrode material for a magnesium battery, comprising a metal oxide as described in any of [1] to [4] or [9].

[14] An active material layer for a positive electrode material for a magnesium battery, comprising the positive electrode material described in

[13] .

[15] A positive electrode for a magnesium battery comprising an active material layer of the positive electrode material described in

[14] and a current collector.

[16] A magnesium battery comprising the positive electrode for magnesium batteries described in

[15] , the negative electrode for magnesium batteries, and an electrolyte. [Effects of the Invention]

[0012] The object of the present invention is to provide a carbon dioxide reduction catalyst capable of reducing carbon dioxide under mild conditions, a carbon dioxide reduction method using the carbon dioxide reduction catalyst, and a carbon dioxide reduction apparatus. Another object of the present invention is to provide a method for producing a catalyst under low-temperature conditions. From the viewpoint of overall energy consumption, including the catalyst production and carbon dioxide reduction processes, carbon dioxide can be reduced with less energy. [Brief explanation of the drawing]

[0013] [Figure 1] This is a transmission electron microscope (TEM) image of the metal oxide obtained in Example 1. [Figure 2]X-ray diffraction (XRD) patterns of the metal oxides obtained in Examples 1 to 7 and Comparative Examples 1 to 3. In FIG. 2, the X-ray diffraction (XRD) patterns of Examples 1 to 7 and Comparative Examples 1 to 3 are Patterns a to j, respectively. [Figure 3] It is a schematic diagram for explaining an example of a reaction for reducing carbon dioxide using the carbon dioxide reduction catalyst containing the metal oxide of this embodiment. [Figure 4] In Example 10, it is a figure for evaluating the charge and discharge characteristics of a magnesium secondary battery prepared using the metal oxide of this embodiment. [Figure 5] It is an X-ray diffraction (XRD) pattern of the metal oxide obtained in Example 11. [Mode for Carrying Out the Invention]

[0014] Hereinafter, embodiments of the metal oxide of the present invention, its manufacturing method, carbon dioxide reduction method, and carbon dioxide reduction apparatus will be described in detail. Note that the present invention is not limited only to the embodiments shown below.

[0015] [Metal Oxide] The metal oxide of this embodiment has a spinel-type crystal structure composed of a metal element A, manganese, and oxygen. The A is at least one metal element selected from the group consisting of nickel, magnesium, zinc, copper, and iron, and preferably, the A is at least one metal element selected from the group consisting of nickel and copper. In the metal oxide, the molar composition ratio of manganese to oxygen is 1:1.8 to 1:2.2, and the molar composition ratio of the metal element A to manganese is 1:1.7 to 1:2.3. In the X-ray diffraction pattern obtained by X-ray diffraction measurement using Cu-Kα rays, the intensity ratio (I 18° / I 37° ) of the peak (P 18° ) with a 2θ value in the range of 16° to 20° and the peak (P 37° ) with a 2θ value in the range of 35° to 39° is 0.2 or more.

[0016] [Composition] In the metal oxide of this embodiment, the molar composition ratio of manganese to oxygen is preferably 1:1.9 to 1:2.1, more preferably 1:1.95 to 1:2.05, and even more preferably 1:2. In the metal oxide of this embodiment, the molar composition ratio of metal element A to manganese is preferably 1:1.8 to 1:2.2, more preferably 1:1.9 to 1:2.1, and even more preferably 1:2.

[0017] In the metal oxide of this embodiment, it is preferable that the molar composition ratio of manganese to oxygen is 1:2, and the molar composition ratio of metal element A to manganese is 1:1.8 to 1:2.2; it is more preferable that the molar composition ratio of manganese to oxygen is 1:2, and the molar composition ratio of metal element A to manganese is 1:1.9 to 1:2.1; and it is even more preferable that the molar composition ratio of manganese to oxygen is 1:2, and the molar composition ratio of metal element A to manganese is 1:2.

[0018] The metal oxide of this embodiment preferably contains a compound represented by formula (1). More preferably, it is a compound represented by formula (1). AMn2O4(1) (In formula (1), A is the same as the aforementioned metal element A.)

[0019] In the metal oxide of this embodiment, it is preferable that the metal element A is nickel. The metal oxide of this embodiment preferably contains a compound represented by formula (2). More preferably, it is a compound represented by formula (2). NiMn2O4(2)

[0020] [Crystal structure] The metal oxide in this embodiment is not particularly limited, but it is preferably 0.5 to 10 nm in average particle size, more preferably 0.5 to 5 nm, and even more preferably 0.5 to 3 nm. Known methods can be used to evaluate the average particle size. For example, it can be evaluated using a scanning electron microscope (SEM) or a transmission electron microscope (TEM). For instance, nanoparticles of 2-5 nm were observed in the TEM image of the metal oxide in Example 1 described later in Figure 1. Furthermore, the average particle size here refers to the primary particle size of the metal oxide. When the metal oxide is in powder form, the particle size of the powder is the secondary particle size, as primary particles are formed by aggregation and other processes.

[0021] The X-rays used for the powder X-ray diffraction pattern of the metal oxide in this embodiment are preferably Cu-kα characteristic X-rays. When the metal element A of the metal oxide in this embodiment is, for example, nickel, the X-ray diffraction pattern line has a peak (P) around 18°, where the 2θ value is in the range of 16° to 20°, as shown in pattern a of Figure 2. 18° ) is observed. A peak (P) is observed around 37°, where the 2θ value is in the range of 35° to 39°. 37° A peak (P) is observed around 18°. 18° ) and a peak around 37° (P 37° The peak shape is broad. Also, in the powder X-ray diffraction pattern of the metal oxide of this embodiment, when metal element A is nickel, a peak (P) appears around 18°. 18° ) and a peak around 37° (P 37° ) and the intensity ratio (I 18° / I 37° ) is 0.2 or higher. Preferably it is 0.3 or higher, more preferably 0.5 or higher, and even more preferably 0.8 or higher. Preferably it is 3.0 or lower, more preferably 2.5 or lower, and even more preferably 2.0 or lower. In this embodiment, if the metal element A of the metal oxide is, for example, copper, the X-ray diffraction pattern shows a peak around 18°, where the 2θ value is in the range of 16° to 20°, as shown in Figure 5 (P 18° ) is observed. A peak (P) is observed around 37°, where the 2θ value is in the range of 35° to 39°. 37° A peak (P) is observed around 18°. 18° ) and a peak around 37° (P 37°The peak shape is broad. Also, in the powder X-ray diffraction pattern of the metal oxide of this embodiment, when metal element A is copper, there is a peak (P) around 18°. 18° ) and a peak around 37° (P 37° ) and the intensity ratio (I 18° / I 37° ) is 0.2 or higher. Preferably it is 0.25 or higher, and more preferably 0.3 or higher. Preferably it is 2.0 or lower, and more preferably 1.5 or lower.

[0022] In the present invention, the peak intensity ratio (I 18° / I 37° For example, the ratio of peak heights can be used. Alternatively, the peak intensity ratio (I 18° / I 37° For example, the ratio of the integrated area of ​​the peaks can be used. Due to the difficulty of evaluation, it is preferable to use the ratio of the peak heights. That is, when metal element A is nickel, a peak (P) will appear around 18°. 18° ) and a peak around 37° (P 37° ) Ratio of height (I 18° / I 37° ) is 0.2 or higher. Preferably it is 0.3 or higher, more preferably 0.5 or higher, and even more preferably 0.8 or higher. Preferably it is 3.0 or lower, more preferably 2.5 or higher, and even more preferably 2.0 or higher. When metal element A is copper, there is a peak (P) around 18°. 18° ) and a peak around 37° (P 37° ) Ratio of height (I 18° / I 37° ) is 0.2 or higher. Preferably it is 0.25 or higher, and more preferably 0.3 or higher. Preferably it is 2.0 or lower, and more preferably 1.5 or lower.

[0023] Known methods exist for determining peak height from X-ray diffraction patterns. For example, a predetermined peak height may be measured using processing software attached to an X-ray diffraction pattern measuring device. For example, in Example 1 described later, the peak height of the X-ray diffraction pattern a in Figure 2 can be measured using commercially available graph analysis software, and the ratio of these peak heights is used to determine a peak (P) around 18°. 18° ) and a peak around 37° (P 37° ) and the intensity ratio (I 18° / I 37° ) was 1.2.

[0024] The metal oxide of this embodiment exhibits a peak (P) in the X-ray diffraction pattern obtained by X-ray diffraction measurement using Cu-Kα rays, where the 2θ value is in the range of 16 to 20 degrees. 18° The full width at half maximum (FWHM) of the material is preferably 1.0° to 7.0°, and more preferably 3.0° to 7.0°. The reason why the X-ray diffraction pattern of the metal oxide in this embodiment shows broad peaks is unknown at the time of filing. It is presumed to be due to the low-temperature manufacturing process, which yields extremely small crystals of a few nanometers. Furthermore, due to the low-temperature manufacturing process, it is presumed to be due to the metal oxide in a low-temperature metastable phase rather than a high-temperature stable phase.

[0025] [Methods for producing metal oxides] Next, the method for producing the metal oxide according to this embodiment will be described. The method for producing metal oxides according to this embodiment includes the following first and second steps, preferably including the first to third steps, and more preferably including the first to fourth steps.

[0026] [1st process] In this process, a mixture containing permanganate, a metal salt of metal element A, and alcohol is prepared. The molar ratio (A:Mn) of the amount of metal salt of metal element A to the amount of permanganate charged is 1:1.7 to 1:2.3. A ratio of 1:1.9 to 1:2.1 is more preferable, and a ratio of 1:2 is even more preferable.

[0027] The permanganate used in this embodiment is not particularly limited as long as it has a certain degree of solubility in the alcohol used. For example, it is preferable that it has a solubility of 10 mmol / L or more. Examples of permanganate used in this embodiment include organic salts of permanganate, such as tetrabutylammonium permanganate. The method for producing the organic salt of permanganate is not particularly limited and can be done by known methods. For example, one method is to obtain the organic salt of permanganate by mixing an aqueous solution of an alkali metal salt of permanganate, such as potassium permanganate, with an aqueous solution of a halogen organic salt, such as tetrabutylammonium bromide.

[0028] The metal salt of metal element A in this embodiment is not particularly limited as long as it has a certain degree of solubility in the alcohol used. For example, it is preferable that the solubility is 10 mmol / L or more. Examples of metal salts of metal element A in this embodiment include halides of metal element A such as nickel chloride and copper chloride. These salts may also be hydrates.

[0029] The alcohol according to this embodiment is not particularly limited as long as it can dissolve at least a portion of the permanganate salt according to this embodiment and the metal salt of metal element A according to this embodiment as a reaction solvent. Examples of alcohols according to this embodiment include monohydric alcohols having a hydroxyl group, such as methanol and ethanol. The alcohol according to this embodiment may contain other components if necessary. For example, ether-based organic solvents such as 2-dimethoxyethane can be used. The ratio of alcohol to other components is not particularly limited and may be 1:10 to 10:1 by volume (v / v), or 1:2 to 2:1. The amount of alcohol used is preferably 10 to 1000 mL.

[0030] In this process, there are no particular limitations on the method for preparing the mixture containing permanganate, a metal salt, and an alcohol. Possible mixing sequences for these reactants include preparing a first mixture of the metal salt and alcohol, then adding permanganate or a permanganate solution to this first mixture, or preparing a first mixture of permanganate and alcohol, then adding a metal salt or permanganate solution to this first mixture. The temperature of these mixtures is not particularly limited, and they may be heated to increase solubility, but it is generally preferable to prepare them at room temperature. There are no particular restrictions on the method or duration of stirring these mixtures, as long as the mixture consisting of permanganate, metal salt, and alcohol temperature is thoroughly mixed.

[0031] [Second process] In this step, the mixture obtained in the first step is stirred and reacted at a temperature below the melting point of the alcohol. The reaction temperature and reaction time are not limited in any particular way and can be appropriately selected, for example, within the range of 10°C to the boiling point of the solvent used, and within the range of 1 minute to 24 hours, depending on the progress of the reaction. Preferably, the reaction temperature is within the range of 20°C to the boiling point of the solvent used, more preferably 20°C to 50°C, even more preferably 20°C to 30°C, and particularly preferably room temperature (e.g., 25°C). The reaction atmosphere is not particularly limited and may be, for example, air (atmospheric pressure).

[0032] [3rd step] In this step, the reaction solution obtained in the previous second step is filtered to obtain the precursor of the metal oxide. The filtration method is not particularly limited, and known methods can be used. For example, suction filtration can be used. The process may also include washing and drying the precipitate. The washing method is not particularly limited, and pure water, ethanol, or a mixture thereof can be used.

[0033] [4th step] In this step, the precursor obtained in the third step is heat-treated at a temperature of 20°C to 300°C. There are no particular limitations on the heat treatment method; for example, heating in air at 25-300°C for 0.3-5 hours is one possible method.

[0034] [Carbon dioxide reduction catalyst] The carbon dioxide reduction catalyst of this embodiment contains the metal oxide of this embodiment. The metal oxide of this embodiment can be used as a catalyst as is. Each of the embodiments of the metal oxide of this embodiment described above can be used. The carbon dioxide reduction catalyst of this embodiment may include the metal oxide of this embodiment and a catalyst support. Examples of catalyst supports include materials commonly used in metal-based catalysts. The carbon dioxide reduction catalyst of this embodiment may be supported on a carrier. The carrier is preferably made of a material that is inert to the reaction with the catalyst and has excellent chemical stability, such as quartz, glass, alumina, silica, titanium, and copper. The shape of the carrier can be any shape, such as a plate, fiber, sphere, rectangle, or mesh, as long as it allows the carbon dioxide reduction reaction of the present invention to proceed.

[0035] [Methods for reducing carbon dioxide] The carbon dioxide reduction method of this embodiment is a method of reducing carbon dioxide using the metal oxide of this embodiment as a catalyst. That is, it is a method of reducing carbon dioxide by bringing carbon dioxide into contact with the catalyst using the carbon dioxide reduction catalyst of this embodiment described above. In the carbon dioxide reduction method of this embodiment, carbon dioxide is preferably reduced to produce carbon monoxide. Figure 3 is a schematic diagram illustrating an example of a reaction to reduce carbon dioxide using the carbon dioxide reduction catalyst containing a metal oxide according to this embodiment. Figure 3 illustrates and explains one possible mechanism of the reduction reaction. However, the present invention is not limited to this mechanism. Figure 3 shows an example in which NiMn2O4 obtained in the embodiment of the present invention is used as the metal oxide. The above NiMn2O4 can function as a carbon dioxide reduction catalyst. In this example of the mechanism, oxygen ions are removed from NiMn2O4 by heating or the like, as shown in formula (3) below, and oxygen gas is generated. Subsequently, it is thought that the carbon dioxide reduction reaction shown in formula (4) below proceeds when CO2 is reacted with the NiMn2O4, and CO is generated from CO2. NiMn2O4 → NiMn2O 4―σ + δ / 2O2(3) δCO2 + NiMn2O 4―σ → δCO+NiMn2O4(4)

[0036] In this embodiment, an example of reducing carbon dioxide to produce carbon monoxide using the metal oxide has been shown, but the catalytic reactions using the metal oxide of this embodiment are not limited to this. The metal oxide of this embodiment may be used as a catalytic material for other carbon dioxide reduction reactions other than carbon monoxide production, other reduction reactions, and even oxidation reactions.

[0037] The reaction temperature for carbon dioxide reduction is preferably 50 to 300°C, more preferably 100 to 250°C, and even more preferably 100 to 200°C. The reaction apparatus can be, for example, a typical reaction apparatus using a gas and a solid catalyst. The method and rate of introduction of carbon dioxide are not particularly limited and can be appropriately selected depending on the reaction scale.

[0038] The reaction pressure for carbon dioxide reduction is not particularly limited, ranging from 0.1 to 10 5 It is preferably Pa, and more preferably atmospheric pressure.

[0039] The carbon monoxide produced by the carbon dioxide reduction method of this embodiment can be discharged outside the reaction system and used as an industrial raw material.

[0040] [Carbon dioxide reduction device] The carbon dioxide reduction apparatus of this embodiment is an apparatus for reducing carbon dioxide, and comprises a carbon dioxide introduction section, a reaction section equipped with a carbon dioxide reduction catalyst, and a heating section for heating the reaction section. The carbon dioxide reduction catalyst includes various forms of the metal oxide of this embodiment described above. The carbon dioxide introduction section described above is not particularly limited, but for example, a gas introduction section used in a conventional gas reactor can be used. The reaction section equipped with the carbon dioxide reduction catalyst described above is not particularly limited, but for example, a gas-phase reactor using a solid catalyst can be used. The heating section described above is not particularly limited, but various conventional heating methods can be used.

[0041] [Electrode material] The electrode material of this embodiment includes the metal oxide according to this embodiment. For example, the positive electrode material for a magnesium battery includes the metal oxide of this embodiment. It is preferable that the positive electrode active material of the positive electrode material for a magnesium battery is the metal oxide of this embodiment. The following is an example of a positive electrode material for a magnesium battery, but the electrode material of this embodiment is not particularly limited to a positive electrode material for a magnesium battery.

[0042] [Magnesium battery] Because magnesium ions are polyvalent, it has a high electrical capacity per unit volume. In addition, magnesium has a higher melting point than lithium, making it safer, and it also has the advantages of being abundant and inexpensive, with less uneven distribution of resources on Earth. For these reasons, magnesium batteries, which use metallic magnesium as the negative electrode, are attracting attention as a next-generation battery to replace lithium batteries. The magnesium battery of this embodiment includes a positive electrode, a negative electrode, and an electrolyte. Typically, a separator is provided between the positive electrode and the negative electrode. In this embodiment, all devices involving a magnesium reaction at the negative electrode are included in the term "magnesium battery." Specifically, the magnesium reactions mentioned above refer to, for example, the dissolution and deposition of magnesium at the interface between magnesium metal and the electrolyte, the intercalation reaction of magnesium ions in carbon-based materials, the alloying reaction of magnesium with elements such as bismuth, and the absorption and release of magnesium ions in battery materials such as titanium oxide at low potentials, such as 1V or less. Examples of magnesium batteries include primary batteries, secondary batteries, air batteries, and electric double-layer capacitors, with secondary batteries being preferred.

[0043] The magnesium battery using the metal oxide positive electrode material of this embodiment will be described below, using an example of a magnesium secondary battery. The magnesium battery of this embodiment is not particularly limited to a secondary battery.

[0044] Furthermore, there are no restrictions on the shape of the magnesium secondary battery in this embodiment. Examples include coin-shaped, button-shaped, sheet-shaped, stacked, cylindrical, flattened, and rectangular shapes.

[0045] <Positive electrode> The positive electrode according to this embodiment includes a current collector and a positive electrode active material layer formed on its surface. The positive electrode active material layer includes the positive electrode material of this embodiment as the positive electrode active material. It may also further include a conductive additive and a binder.

[0046] "Current collector" The current collector in the positive electrode of the present invention is composed of conductive materials such as platinum, copper, stainless steel (SUS), aluminum, iron, chromium, nickel, titanium, and carbon. Current collectors having shapes such as mesh or sheet are also possible. A specific example of a current collector for the positive electrode is an aluminum mesh.

[0047] "Cathode active material layer" The positive electrode active material layer according to this embodiment includes the positive electrode material of this embodiment as the positive electrode active material. That is, the positive electrode active material layer according to this embodiment includes the metal material of this embodiment as the positive electrode active material. The metal material of this embodiment includes the various preferred embodiments and specific examples described above. It also includes the materials described in the examples described later. The positive electrode active material layer according to this embodiment may also include other positive electrode active materials. The other positive electrode active materials are not particularly limited, and known active materials other than the metal materials of this embodiment that are commonly used as active materials in magnesium batteries can be used. Examples include transition metal oxides; transition metal elements; conductive polymers and their derivatives such as polyacetylene, polyaniline, polypyrrole, polythiophene, and poly(p-phenylene); and disulfide compounds.

[0048] The thickness of the active material layer in the positive electrode of the present invention is not particularly limited, but is usually 1 μm to 1000 μm, preferably 1 μm to 500 μm, and more preferably 1 μm to 300 μm. The content of the electrode material of this embodiment in 100% by mass of the total positive electrode active material in the positive electrode active material layer of this embodiment is 50% by mass or more, preferably 80% by mass or more, and more preferably 90% by mass or more. The content of the metal material of this embodiment in 100% by mass of the electrode material of this embodiment is 80% by mass or more, preferably 90% by mass or more, more preferably 95% by mass or more, and particularly preferably 100%.

[0049] Examples of conductive additives in this embodiment include carbon blacks such as acetylene black, Ketjen black, furnace black, and thermal black. Among these, acetylene black is preferred. The content of the conductive additive is not particularly limited, but for example, it is usually 1% to 50% by mass, preferably 5% to 30% by mass, and more preferably 10% to 20% by mass, relative to the total mass of the positive electrode active material layer. Examples of binders in this embodiment include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), carboxymethylcellulose (CMC), styrene-butadiene copolymer (SBR), acrylonitrile-butadiene copolymer (NBR), polyacrylonitrile (PAN), ethylene vinyl alcohol copolymer (EVOH), polyurethane, polyacrylate, polyvinyl ether, polyamide, and polyimide. The content of the binder is not particularly limited, but for example, it is usually 1% to 50% by mass, preferably 5% to 30% by mass, and more preferably 10% to 20% by mass, relative to the total mass of the positive electrode active material layer. When two or more binders are used in combination, their total mass should be equal to the above content.

[0050] "Method for manufacturing a positive electrode" The positive electrode of the present invention can be manufactured by applying or pressing the positive electrode material composition of this embodiment onto a current collector and drying it. The positive electrode material composition of this embodiment includes the positive electrode material of this embodiment as the positive electrode active material. It may also further include a conductive additive and a binder. In the above manufacturing method, the amount of the positive electrode material composition used in this embodiment can be appropriately set so that the active material layer after drying reaches the desired thickness.

[0051] In the method for manufacturing the positive electrode of this embodiment, the coating of the positive electrode material composition of this embodiment onto the current collector can be carried out in accordance with a known method, and specific coating methods include, for example, a self-propelled coater, an inkjet method, a doctor blade method, a spray method, or a combination thereof.

[0052] In the method for manufacturing the positive electrode of this embodiment, drying of the positive electrode material composition of the present invention on the current collector can be carried out in accordance with known methods, and is usually done by heat treatment. The drying conditions during heating, such as whether or not a vacuum is required, the drying time, and the drying temperature, can be appropriately set according to the amount of the positive electrode material composition of the present invention applied and its volatilization rate. As a specific drying method, for example, drying can be carried out in a vacuum, usually at a temperature of 50°C to 150°C, preferably 70°C to 130°C, for usually 1 hour to 20 hours, preferably 3 hours to 12 hours.

[0053] In the method for manufacturing the positive electrode of this embodiment, a pressing treatment may be performed after drying. Examples of pressing treatments in this embodiment include the calender roll method and the flat plate pressing method, with the calender roll method being preferred.

[0054] <Negative electrode> The negative electrode active material constituting the negative electrode of this embodiment is not particularly limited and includes, for example, metallic magnesium, magnesium-containing alloys, metals or alloys that can be alloyed with magnesium, oxides that can be doped and dedoped with magnesium ions, transition metal nitrides that can be doped and dedoped with magnesium ions, and carbon materials that can be doped and dedoped with magnesium ions. The negative electrode is any suitable electrode configured to adsorb magnesium and release magnesium ions. The negative electrode may also include any suitable active material layer configured to adsorb and release magnesium ions. The active material of the negative electrode is not limited to any particular material.

[0055] <Separator> The separator in this embodiment is not particularly limited as long as it can electrically insulate the negative electrode and the positive electrode so that the non-aqueous electrolyte solution described later can penetrate the separator. Examples of the separator in this embodiment include porous synthetic resin films, such as porous films made of polyolefin polymer. Specifically, examples of porous films include porous films made of polyethylene polymer and porous films made of polypropylene.

[0056] <Electrolyte> The electrolyte in this embodiment is not particularly limited as long as it can guide magnesium ions between the negative and positive electrodes, and any suitable electrolyte such as a non-aqueous magnesium ion conductor may be used. Examples of electrolytes in this embodiment include non-aqueous electrolytes that contain an electrolyte and an organic solvent.

[0057] Examples of solvents in the electrolyte according to the present invention include ether-based solvents such as diethyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, diisopropyl ether, 1,2-dimethoxyethane, diethylene glycol dimethyl ether (diglyme), triethylene glycol dimethyl ether (triglime), and tetraethylene glycol dimethyl ether (tetraglime); halogenated hydrocarbon-based solvents such as dichloromethane and chloroform; carbonate-based solvents such as dimethyl carbonate and diethyl carbonate; nitrile-based solvents such as acetonitrile; and sulfone-based solvents such as sulfolane, dimethyl sulfone, and ethylmethyl sulfone.

[0058] Among these, ether-based solvents and sulfone-based solvents are preferred, with ether-based solvents being preferred. Among these solvents, tetrahydrofuran, 1,2-dimethoxyethane, diglyme, triglyme, tetraglyme, and sulfolane are preferred, tetrahydrofuran, diglyme, triglyme, and tetraglyme are more preferred, and tetrahydrofuran and triglyme are even more preferred. These solvents may also be a mixture of two or more types.

[0059] Examples of electrolytes included in the electrolyte solution of this embodiment include Lewis basic organomagnesium compounds RMgX. Here, R is selected from the group consisting of alkyl ligands such as methyl, ethyl, and butyl, aryl, benzyl, amide, naphthal, phenyl, alkenyl, alkynyl, or derivatives thereof. X is a halide such as F, Cl, Br, or I. In some embodiments, the electrolyte further contains a Lewis acid compound that causes a metal exchange reaction. Examples of Lewis acid compounds, but not limited to these, include AlCl3, BCl3, AlCl2Et, FeCl2, FeCl3, and TiCl4. In some embodiments, the electrolyte further contains a salt. Examples of salts, though not limited to these, include MgCl2, Mg(ClO4)2, Mg(BF4)2, Mg(AsF6)2, Mg(PF6)2, Mg(CF3SO3)2, Mg[N(CF3SO2)2]2, Mg[C(SO2CF3)3]2, LiCl, LiClO4, LiBF4, LiAsF6, LiPF6, Li(CF3SO3), LiN(CF3SO2)2, LiC(SO2CF3)3, NaCl, NaClO4, NaBF4, NaAsF6, NaPF6, Na(CF3SO3), NaN(CF3SO2)2, and NaC(SO2CF3)3.

[0060] The electrolyte of this embodiment may be, for example, a mixture of the following compound A, aluminum compound B, and ether-based solvent C.

[0061] Compound A: B(OMgCl)3,CH3B(OMgCl)2,C2H5B(OMgCl)2,CH3OB(OMgCl)2,C2H5OB(OMgCl)2,C6H5OB(OMgCl)2,C6H5B(OMgCl)2,C6H4 [B(OMgCl)2]2,(C6H4F)B(OMgCl)2,(C6H3F2)B(OMgCl)2,[C6H4(CH3)]B(OMgCl)2,[C6H3(CH3)2]B(OMgCl)2,[C6H4(OC H3)]B(OMgCl)2,[C6H3(OCH3)2]B(OMgCl)2,[C6H4(C6H5)]B(OMgCl)2,[C6H4(OC6H5)]B(OMgCl)2,C10H7B(OMgCl)2,C1 4H9B(OMgCl)2,(C4H3O)B(OMgCl)2,(C4H3S)B(OMgCl)2,(C4H3NH)B(OMgCl)2,(C5H4N)B(OMgCl)2 or (C8H5O)B(OMgCl)2

[0062] Aluminum compound B: Boron(III) chloride, aluminum(III) chloride, methylaluminum dichloride, dimethylaluminum chloride, or triphenylaluminum

[0063] Ether-based solvent C: Tetrahydrofuran, diglyme, triglyme, or tetraglyme.

[0064] A mixture of B(OMgCl)3 or C6H5B(OMgCl)2, aluminum(III) chloride, and tetrahydrofuran, triglyme, or a mixture of these two solvents is preferred. A mixture of B(OMgCl)3, aluminum(III) chloride, and tetrahydrofuran, triglyme, or a mixture of these two solvents is particularly preferred.

[0065] Specific examples of the electrolyte contained in the electrolyte solution of this embodiment include, for example, "MaglutionTMB01" (B(OMgCl)3 - AlCl3 complex (1:6) / triglyme solution), "MaglutionTMB02" (B(OMgCl)3 - AlCl3 complex (1:6) / triglyme - tetrahydrofuran (50:50 vol%) solution) manufactured by Fujifilm Wako Pure Chemical Corporation, MgTFSA2 (Mg[N(CF3SO2)2]2) / triglyme solution manufactured by Kishida Chemical Co., Ltd., and the like.

Example

[0066] Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited by these examples.

[0067] (Raw materials) Nickel chloride hexahydrate: Fujifilm Wako Pure Chemical Corporation, 98.0+% Copper acetate hydrate: Fujifilm Wako Pure Chemical Corporation, 98.0+% Potassium permanganate: Fujifilm Wako Pure Chemical Corporation, 99.3+% Tetrabutylammonium bromide: TCI, >98.0% Methanol: Fujifilm Wako Pure Chemical Corporation Ethanol: Fujifilm Wako Pure Chemical Corporation 1,2 - Dimethoxyethane: Kanto Chemical Co., Inc.

[0068] (Evaluation method) <Transmission electron microscope (TEM)> Equipment: EM - 002B (Topcon)

[0069] <X - ray diffraction method> Equipment: D2 PHASER XE - T EDITION (Bruker) Light source: Cu - Kα Holder: Silicon non - reflective sample holder Divergence slit: 1 mm Solar slit: 2.5° Air scatter screen: 3 mm [[ID= <Method for Measuring Specific Surface Area> BET specific surface area: BET method by physical adsorption of inert gas at low temperature and low humidity Measuring device: BELSORP-mini II Measurement conditions: N2

[0071] <Method for Measuring CO Concentration: Gas Chromatography Method> Device: Sensor Gas Chromatograph Detector: Semiconductor

[0072] (Synthesis Example 1) 「Synthesis of Tetrabutylammonium Permanganate」 3.16 g of potassium permanganate was dissolved in 100 mL of pure water to prepare an aqueous solution of potassium permanganate. 6.45 g of tetrabutylammonium bromide was dissolved in 50 mL of pure water to prepare an aqueous solution of tetrabutylammonium bromide. The aqueous solution of tetrabutylammonium bromide was added dropwise to the aqueous solution of potassium permanganate while stirring, and after stirring for 1 hour, the generated precipitate was suction filtered. The obtained precipitate was washed with 200 mL of pure water and dried under reduced pressure at 25 °C to obtain 6 g of tetrabutylammonium permanganate.

[0073] 「Preparation of Metal Oxide and XRD Evaluation」 (Example 1) 475 mg of nickel chloride hexahydrate was dissolved in a mixed solvent of 25 mL of methanol and 25 mL of 1,2-dimethoxyethane to prepare a first mixed solution. 723 mg of tetrabutylammonium permanganate obtained in Synthesis Example 1 was added once to the first solution to obtain a second mixed solution. The second mixed solution was stirred at 25 °C for 1 hour to generate a precipitate and obtain a third mixed solution. The precipitate obtained by suction filtering the third mixed solution was washed in the order of 300 mL of pure water and 300 mL of ethanol and dried at 100 °C for 12 hours. Then, it was held at 25 °C for 2 hours. 200 mg of NiMn2O4 powder (NMO-1) of this example was obtained. TEM and XRD measurements were performed on the NiMn2O4 powder (NMO-1) of this example. The results are shown in Fig. 1 and Fig. 2 (pattern a).

[0074] (Examples 2-7) In Examples 2 to 7, instead of holding the samples in an air atmosphere at 25°C for 2 hours, they were held at 100°C, 150°C, 200°C, 250°C, 300°C, and 350°C, respectively, for 2 hours. Otherwise, 200 mg of NiMn2O4 powder (NMO-2) to powder (NMO-7) was obtained in the same manner as in Example 1. XRD measurements were performed on the NiMn2O4 powders (NMO-2) to (NMO-7) of Examples 2 to 7. The results are shown in Figure 2 (in Figure 2, patterns b to g are shown for NMO-2 to NMO-7, respectively).

[0075] (Comparative Examples 1-3) In Comparative Examples 1 to 3, 200 mg of the metal oxide powder (cNMO-1) to powder (cNMO-3) was obtained in the same manner as in Example 1, except that instead of being held at 25°C for 2 hours as in Example 1, the samples were held at 400°C, 600°C, and 800°C for 2 hours, respectively. XRD measurements were performed on the metal oxide powders (cNMO-1) to (cNMO-3) of Comparative Examples 1 to 3. The results are shown in Figure 2 (in Figure 2, patterns h to j are shown for cNMO-1 to NMO-3, respectively).

[0076] "Carbon dioxide reduction reaction" (Example 8) 100 mg of the NiMn2O4 powder sample (NMO-2) obtained in Example 2 was weighed and placed in a thermogravimetric analyzer. While circulating carbon dioxide (at a flow rate of 100 ml / min or less, with a CO2 concentration of 99.9%), the sample was maintained at 100°C in the attached electric furnace. After 150 minutes, the CO concentration in the gas after circulation (units: volume ppm or mass ppm) was measured by gas chromatography. The results are shown in Table 1.

[0077] Furthermore, while circulating carbon dioxide, the powder sample (NMO-2) was held at 100°C in an electric furnace for 1000 minutes, and then cooled to room temperature. The powder sample (NMO-2') after the reaction was removed. The specific surface area of ​​the powder sample before the reaction (NMO-2) and the powder sample after the reaction (NMO-2') was measured. The results are shown in Table 2. Furthermore, XRD measurements were performed on the powder sample after the reaction (NMO-2'). The results were the same as those for the powder sample before the reaction (NMO-2).

[0078] (Examples 9 and 10) The CO concentration in the gas after flow was measured using the same method as in Example 8, except that instead of being held at 100°C in the electric furnace, it was held at 250°C and 350°C. The results are shown in Table 1.

[0079] (Comparative Example 4) The CO concentration in the gas after flow was measured using the same method as in Example 8, except that instead of weighing 100 mg of NiMn2O4 powder sample (NMO-1) prepared at 25°C and placing it in the thermogravimetric analyzer, the sample was left blank (blank: no sample). The results are shown in Table 1.

[0080] (Consideration) A comparison of the CO concentrations in Comparative Example 4 (Blank) and Example 8 (100°C) revealed that the CO concentrations in Examples 6 and 7, which incorporated the metal oxide of this embodiment, were clearly increased. This indicates that carbon dioxide could be converted to carbon monoxide using the NiMn2O4 powder sample (NMO-1) prepared at 25°C.

[0081] Furthermore, the CO concentration increased in Examples 9 (250°C) and 10 (350°C) compared to Example 8 (100°C). This is thought to be due to an increased reaction rate from carbon dioxide to CO due to the high-temperature process. On the other hand, the CO concentration decreased in Example 10 (350°C) compared to Example 9 (250°C). Despite the increased reaction rate due to the higher reaction temperature, the amount of carbon dioxide converted decreased. The main reason is thought to be that at 350°C, as shown in Figure 2 (pattern g) of Example 7, the NiMn2O4 powder (NMO-1) obtained in Example 1 changed to the metal oxide (NMO-7) obtained in Example 7. Therefore, it is presumed that the catalytic effect on the reaction to reduce carbon dioxide weakened.

[0082] Based on experimental results at the time of filing, the NiMn2O4 powder samples (NMO-1) to (NMO-7) of Examples 1 to 7, which are metal oxides of this embodiment, showed broad peaks as shown in the XRD patterns a to e in Figure 2. The XRD patterns h and i in Figure 2 of Comparative Examples 1 and 2 match the XRD patterns of NiMnO3 crystals, and the XRD pattern j in Figure 2 of Comparative Example 3 matches the XRD pattern of NiMn2O4 crystals, which are spinel crystals. It is presumed that the NiMn2O4 powder samples of Examples 1 to 7 are spinel crystals, which are low-temperature metastable phases, compared to the high-temperature stable phase of Comparative Example 3. In other words, in Example 7 (350°C), a phase change began until it no longer corresponds to a low-temperature metastable phase like the metal oxides of this embodiment, and it is thought that the performance of the catalyst itself decreased.

[0083] [Table 1]

[0084] [Table 2]

[0085] [Fabrication of a magnesium battery using the positive electrode active material of this embodiment] (Example 10) A positive electrode material composition was prepared by mixing 60 parts by mass of NiMn2O4 powder (NMO-1) obtained in Example 1, 30 parts by mass of acetylene black (conductive additive: FX-35, manufactured by Denka Co., Ltd.), and 10 parts by mass of polytetrafluoroethylene (binding agent: 6-J, Mitsui Chemicals). Using the positive electrode material composition, a positive electrode material active material layer (thickness: approximately 30 μm) was pressed onto a current collector made of aluminum mesh (Nirako, 100 mesh), and a positive electrode was fabricated by vacuum heat treatment at 100°C for 12 hours. The positive electrode, negative electrode, reference electrode, and electrolyte were set in a 2032 type coin cell in a glove box filled with argon gas to fabricate a magnesium battery. A metallic magnesium foil was used for the negative electrode, and a Mg[N(CF3SO2)2]2 / triglyme solution was used for the electrolyte. The Mg[N(CF3SO2)2]2 / triglyme solution was prepared by dissolving MgTFSA2 (magnesium bis(trifluoromethanesulfonyl)amide, Kishida Chemical) in triglyme (Kanto Chemical) at a concentration of 0.3 M. The current density of the prepared battery was 10 mA. -1 A charge-discharge test was conducted at an operating temperature of 50°C. The evaluation results are shown in Figure 4.

[0086] (Example 11) Except for using 199 mg of copper acetate hydrate instead of 475 mg of nickel chloride hexahydrate, 200 mg of the CuMn2O4 powder (CMO-1) of this example was obtained in the same manner as in Example 1. XRD measurements were performed on the CuMn2O4 powder (CMO-1) of this example. The results are shown in Figure 5.

Claims

1. A metal oxide having a spinel-type crystal structure, comprising nickel, manganese, and oxygen, The molar composition ratio of manganese to oxygen is 1:1.8 to 1:2.

2. The molar composition ratio of nickel to manganese is 1:1.7 to 1:2.

3. The average particle size is 1 to 10 nm. In the X-ray diffraction pattern obtained by X-ray diffraction measurement using Cu-Kα rays, the aforementioned metal oxide is Peaks (P) where the 2θ value is in the range of 16° to 20° １８° ) and the peak (P) where the 2θ value is in the range of 35° to 39°. ３７° ) and the intensity ratio (I １８° / I ３７° ) is 0.2 or greater, The full width at half maximum (FWHM) of the peak (P 18°) where the 2θ value is in the range of 16 to 20 degrees is 1.0° to 7.0°. A metal oxide characterized by the following features.

2. The metal oxide according to claim 1, comprising a compound represented by formula (1). NiMn ２ O ４ (1)

3. A method for producing a metal oxide having a spinel-type crystal structure, comprising metal element A, manganese, and oxygen, The above A is at least one metallic element selected from the group consisting of nickel and copper. The molar composition ratio of manganese to oxygen is 1:1.8 to 1:2.

2. The molar composition ratio of metal element A to manganese is 1:1.7 to 1:2.

3. The metal oxide has a peak (P １８° ) with a 2θ value in the range of 16° to 20° and a peak (P ３７° ) with a 2θ value in the range of 35° to 39° in the X-ray diffraction pattern obtained by X-ray diffraction measurement using Cu-Kα rays. The intensity ratio (I １８° / I ３７° ) is 0.2 or more, A first step involves preparing a mixture containing permanganate, a metal salt of the aforementioned metal element A, and an alcohol. The mixture obtained in the first step is reacted by stirring it at a temperature below the melting point of the alcohol in the second step, and includes, The above A is at least one metallic element selected from the group consisting of nickel and copper. The molar ratio (A:Mn) of the amount of metal salt of metal element A charged to the amount of permanganate charged, in terms of metal elements, is 1:1.7 to 1:2.

3. A method for producing metal oxides, characterized by the following:

4. A method for producing a metal oxide having a spinel-type crystal structure, comprising metal element A, manganese, and oxygen, A first step involves preparing a mixture containing permanganate, a metal salt of the aforementioned metal element A, and an alcohol. The mixture obtained in the first step is reacted by stirring it at a temperature below the melting point of the alcohol in the second step, and includes, The above A is at least one metallic element selected from the group consisting of nickel and copper. The molar ratio (A:Mn) of the amount of metal salt of metal element A charged to the amount of permanganate charged, in terms of metal elements, is 1:1.7 to 1:2.

3. A method for producing metal oxides, characterized by the following:

5. The aforementioned permanganate is tetrabutylammonium permanganate. The method for producing a metal oxide according to claim 3 or 4, wherein the metal salt is at least one selected from the group consisting of nickel chloride and copper chloride.

6. A third step involves filtering the reaction solution obtained in the second step to obtain the metal oxide precursor, A fourth step involves heat-treating the precursor obtained in the third step at a temperature of 20°C to 300°C, A method for producing a metal oxide according to any one of claims 3 to 5, further comprising:

7. A carbon dioxide reduction catalyst comprising the metal oxide described in claim 1 or 2.

8. A method for reducing carbon dioxide using a metal oxide as a catalyst according to claim 1 or 2, A method for reducing carbon dioxide, characterized in that the reaction temperature in the carbon dioxide reduction reaction is 50°C or higher and 300°C or lower.

9. A carbon dioxide reduction device that reduces carbon dioxide, The carbon dioxide inlet and A reaction section equipped with a carbon dioxide reduction catalyst, A heating section for heating the above reaction section, Equipped with, The carbon dioxide reduction catalyst comprises the metal oxide described in claim 1 or 2. A carbon dioxide reduction device characterized by the following features.

Images